The present invention relates to a mold assembly for forming a contact lens blank or workpiece and a method of producing a contact lens from the formed lens blank. More specifically, the present invention is concerned with such a mold assembly for forming the lens blank, which is subsequently subjected to a cutting operation to form a base or rear curved surface and a front curved surface of an intended contact lens. The invention also relates to a method of producing a contact lens from the lens blank obtained by the mold assembly, by cutting the lens blank.
Discussion of the Related Art
A contact lens is generally fabricated from a contact lens material which is formed into a cylindrical shape by polymerization of a monomer liquid in a test tube. The conventional cylindrical contact lens material is first subjected to a turning operation with a cutting tool in the axial direction with a suitable depth of cut, so as to reduce its outside diameter, so that a bar-shaped blank having a high degree of cylindricity is obtained. Then, the thus obtained bar-shaped blank is cut into a plurality of workpieces (lens blanks) by a cut-off tool, so that each of the workpieces has a predetermined axial dimension. Each workpiece thus obtained is subjected to cutting operations to provide a desired contact lens. Namely, one of the opposite end surfaces of the workpiece is cut into a base or rear curved surface of the contact lens, i.e., an inner surface of the contact lens which is to be held in contact with the cornea of an eye, while the other end surface of the workpiece is cut into a front curved surface of the contact lens, i.e., an outer surface of the contact lens opposite to the cornea-contacting surface.
The above method, however, suffers from a problem that a large amount of the expensive contact lens material is discarded as a waste during the cutting operations, whereby the cost of the material is inevitably increased. In addition, the polymer composition of the cylindrical contact lens material is not uniform in its longitudinal direction due to a variation of the composition of the monomer liquid during the polymerization. Accordingly, the workpieces obtained by cutting the bar-shaped blank undesirably have different material compositions.
In the method as described above, the rear curved surface and the front curved surface of the contact lens are formed by cutting operations on the workpiece (lens blank).
Another method of producing a contact lens is disclosed in JP-A-57-608, JP-A-64-500256 and JP-A-4-290706, for instance, wherein a mold having a mold cavity which corresponds to a profile of the intended contact lens. More specifically described, a monomer liquid injected into the mold cavity is polymerized, so as to mold the contact lens having the profile corresponding to the shape of the mold cavity. In this method, the front and rear curved surfaces of the contact lens are formed simultaneously upon the polymerization of the monomer liquid within the mold.
In the molding method as described above, however, if the monomer liquid comprises a plurality of monomer components, each of the monomer components and the material of the mold undesirably interact with each other upon the polymerization of the monomer liquid in the mold cavity. In this case, the obtained contact lens has different compositions at its inner portion and its outer or surface portion which was held in contact with the molding surfaces of the mold, making it difficult to assure uniform or homogeneous quality of the obtained contact lens. Further, this molding method is not efficient in producing various kinds of contact lenses having different configurations.
Another method of producing a contact lens is disclosed in JP-B-59-8219, JP-B-3-76213, JP-B-4-11085, JP-A-7-080860, and JP-A-8-25378, for instance, wherein one of the front and rear curved surfaces of the intended contact lens is formed during polymerization of the monomer liquid within the mold cavity, while the other curved surface is formed by a cutting operation. In this method, too, since one of the front and rear curved surfaces is formed during the polymerization of the monomer liquid, so as to have a configuration corresponding to that of the molding surface, the obtained contact lens suffers from different compositions at its surface and inner portions due to a variation of the monomer composition caused by the interaction with the material of the mold.